Agricultural harvesters are comprised of a self propelled agricultural harvesting vehicle often called a “combine” that supports an agricultural harvesting head also known as a “header”. The header separates the crop from the ground and carries it rearward through an opening in the header. The crop is then sent to the agricultural harvesting vehicle where it is threshed, separated, and cleaned.
For many crops, it is important for the header to travel very close to the ground so it collects all the crop that is being harvested. This is particularly important for crops such as soybeans, which are small bush-like plants only a foot or two high. For crops like these, the header is often positioned to drag along the ground itself, or bounce slightly over the surface of the ground to ensure that it captures all of the crop. One of the dangers of operating a header this close to the ground is the risk that will run into the ground or an obstruction of on the ground and be damaged.
Other crops, like wheat or corn, are much taller. The crop portions of these plants are carried much higher in the air. To harvest these crops, the header can be operated relatively high in the air away from any obstructions. The risk of colliding with the ground is limited, and the agricultural harvester can therefore be operated at a higher speed of travel through the field.
Different control systems are used to control the height of the header above the ground.
In one system such as US2011/0154795, a height sensor is disclosed that generates a signal indicating the distance between the bottom of the header and the ground and provides a feedback signal to control the height of header 104. If the height sensor shows that the header is too close to the ground, a control circuit energizes actuators that lift the header until the appropriate height is reached.
In another system, the fluid pressure in the hydraulic or pneumatic members that support the header and raise it up and down is monitored. When this pressure decreases, it indicates that the header is running into the ground. A control circuit then raises the header until the pressure returns to its nominal value indicating that the header is being supported above the ground.
Neither of these control systems is sufficient to control the header height over a wide range of header heights.
What is needed is a control system that will provide more accurate control of header height over a wider range of height settings.
The invention described in claim 1 of this application provides that benefit. The other arrangements described in the dependent claims provide additional advantages that are discussed below.